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Journal ArticleDOI

Geomagnetic secular variation and the statistics of palaeomagnetic directions

TL;DR: In this paper, the role of palaeosecular variation (PSV) in the use of statistics for palaeomagnetic studies is examined and new reliability criteria for the reliability of a data set are provided.
Abstract: In this study, we examine the role of palaeosecular variation (PSV) in the use of statistics for palaeomagnetic studies, and we provide new reliability criteria for palaeomagnetic poles or directions.We first conclude that Fisher statistics should not be applied to average palaeomagnetic directions but to virtual geomagnetic pole (VGP) distributions instead. Secondly, we strongly advocate that typical properties of geomagnetic field behaviour are taken into account in the assessment of palaeomagnetic data sets. The latitude-dependent properties (E, S, k) provide useful guidelines for the reliability of a palaeomagnetic data set. A reliable assessment of these properties depends on the (sufficient) number of palaeomagnetic samples being taken. Therefore, as an additional instrument of assessing data sets, we provide a N-dependent A95 envelope, bounded by an upper limit A95max, and a lower limit A95min that helps to ascertain whether or not a distribution has sufficiently well-sampled PSV and therefore geomagnetic field behaviour. Applying these criteria is indispensable for studies of geomagnetic behaviour, or for studies aiming at using TK03.GAD for inclination error correction through the elongation/inclination (E/I) method. For palaeomagnetic studies aimed at geological reconstructions, they form helpful guidelines and increase the confidence in the rocks having faithfully recorded the field. An analysis of published Eastern Mediterranean data shows that the vast majority of studies do not conform to the Van der Voo criteria, in particular with respect to N and A95. We have provided criteria that are on the one hand more lenient (lower N may still provide relevant information), and on the other hand more strict (for high N the criterion of A95 < 16° should be adapted to a requirement of lower A95, e.g. A95 80).

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Journal ArticleDOI
TL;DR: It is suggested that the approximately 50 Ma “India”–Asia collision was a collision of a Tibetan-Himalayan microcontinent with Asia, followed by subduction of the largely oceanic Greater India Basin along a subduction zone at the location of the Greater Himalaya.
Abstract: Cenozoic convergence between the Indian and Asian plates pro- duced the archetypical continental collision zone comprising the Himalaya mountain belt and the Tibetan Plateau. How and where India-Asia convergence was accommodated after collision at or be- fore 52 Ma remains a long-standing controversy. Since 52 Ma, the two plates have converged up to 3,600 35 km, yet the upper crustal shortening documented from the geological record of Asia and the Himalaya is up to approximately 2,350-km less. Here we show that the discrepancy between the convergence and the shortening can be explained by subduction of highly extended continental and oceanic Indian lithosphere within the Himalaya be- tween approximately 50 and 25 Ma. Paleomagnetic data show that this extended continental and oceanic "Greater India" promontory resulted from 2,675 700 km of North-South extension between 120 and 70 Ma, accommodated between the Tibetan Himalaya and cratonic India. We suggest that the approximately 50 Ma "India"- Asia collision was a collision of a Tibetan-Himalayan microconti- nent with Asia, followed by subduction of the largely oceanic Greater India Basin along a subduction zone at the location of the Greater Himalaya. The "hard" India-Asia collision with thicker and contiguous Indian continental lithosphere occurred around 25-20 Ma. This hard collision is coincident with far-field deforma- tion in central Asia and rapid exhumation of Greater Himalaya crys- talline rocks, and may be linked to intensification of the Asian monsoon system. This two-stage collision between India and Asia is also reflected in the deep mantle remnants of subduction imaged with seismic tomography.

566 citations


Cites background or methods from "Geomagnetic secular variation and t..."

  • ...This filtering procedure is commonly used by the geomagnetic field community (10, 11)....

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  • ...The onset of this last phase of India–Asia collision is contemporaneous with a period of outward growth and extension of the Tibetan plateau (10, 12, 48)....

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Journal ArticleDOI
10 Jun 2015-PLOS ONE
TL;DR: It is shown that using a mantle reference frame, which defines plate positions relative to the mantle, instead of a paleomagnetic reference frame may introduce errors in paleolatitude of more than 15° (>1500 km), because mantle reference frames cannot constrain, or are specifically corrected for the effects of true polar wander.
Abstract: Realistic appraisal of paleoclimatic information obtained from a particular location requires accurate knowledge of its paleolatitude defined relative to the Earth’s spin-axis. This is crucial to, among others, correctly assess the amount of solar energy received at a location at the moment of sediment deposition. The paleolatitude of an arbitrary location can in principle be reconstructed from tectonic plate reconstructions that (1) restore the relative motions between plates based on (marine) magnetic anomalies, and (2) reconstruct all plates relative to the spin axis using a paleomagnetic reference frame based on a global apparent polar wander path. Whereas many studies do employ high-quality relative plate reconstructions, the necessity of using a paleomagnetic reference frame for climate studies rather than a mantle reference frame appears under-appreciated. In this paper, we briefly summarize the theory of plate tectonic reconstructions and their reference frames tailored towards applications of paleoclimate reconstruction, and show that using a mantle reference frame, which defines plate positions relative to the mantle, instead of a paleomagnetic reference frame may introduce errors in paleolatitude of more than 15° (>1500 km). This is because mantle reference frames cannot constrain, or are specifically corrected for the effects of true polar wander. We used the latest, state-of-the-art plate reconstructions to build a global plate circuit, and developed an online, user-friendly paleolatitude calculator for the last 200 million years by placing this plate circuit in three widely used global apparent polar wander paths. As a novelty, this calculator adds error bars to paleolatitude estimates that can be incorporated in climate modeling. The calculator is available at www.paleolatitude.org. We illustrate the use of the paleolatitude calculator by showing how an apparent wide spread in Eocene sea surface temperatures of southern high latitudes may be in part explained by a much wider paleolatitudinal distribution of sites than previously assumed.

393 citations


Cites background from "Geomagnetic secular variation and t..."

  • ...several hundreds of kilometers in paleolatitude), following clear quality criteria [23]....

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Journal ArticleDOI
TL;DR: In this paper, the authors use advances made in kinematic restoration software in the last decade with a systematic reconstruction protocol for developing a more quantitative restoration of the Mediterranean region for the last 240 million years.

286 citations

Journal ArticleDOI
TL;DR: A module to visualize VGPs and expected paleolatitudes, declinations, and inclinations relative to widely used global apparent polar wander path models in coordinates of major continent-bearing plates is provided.

175 citations


Cites background or methods from "Geomagnetic secular variation and t..."

  • ...It has long been recognized (e.g. Creer, 1962; Cox, 1970) and later re-emphasized (e.g. Tauxe et al., 2008, Tauxe et al., 2010; Deenen et al., 2011) that the scatter of directional data induced by paleo-secular variation becomes increasingly N–...

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  • ...Creer, 1962; Cox, 1970) and later re-emphasized (e.g. Tauxe et al., 2008, Tauxe et al., 2010; Deenen et al., 2011) that the scatter of directional data induced by paleo-secular variation becomes increasingly N–S elongated with lower latitudes....

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  • ...In particular, the behavior of the magnetic field known as paleo-secular variation, but also measurement uncertainties, induce scatter in paleomagnetic data (e.g., Butler, 1992; Johnson et al., 2008, Biggin et al., 2008, Tauxe et al., 2010, Deenen et al., 2011)....

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  • ...Since the actual data in paleomagnetic research are seldom published or included in databases, and commonly only site mean directions are given, most published sedimentary paleomagnetic data include statistical parameters of direction distributions (α95, k) that are unrepresentative of the dataset (Deenen et al., 2011)....

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  • ...…in paleomagnetic research are seldom published or included in databases, and commonly only site mean directions are given, most published sedimentary paleomagnetic data include statistical parameters of direction distributions (α95, k) that are unrepresentative of the dataset (Deenen et al., 2011)....

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Book ChapterDOI
01 Aug 2014
TL;DR: In this article, published paleomagnetic data from well-dated sedimentary rocks and lavas from the Lhasa terrane have been reevaluated in a statistically consistent framework to assess the latitude history of southern Tibet from ca. 110 Ma to the present.
Abstract: Published paleomagnetic data from well-dated sedimentary rocks and lavas from the Lhasa terrane have been reevaluated in a statistically consistent framework to assess the latitude history of southern Tibet from ca. 110 Ma to the present. The resulting apparent polar wander path shows that the margin of the Lhasa terrane has remained at lat ∼20° ± 4°N from ca. 110 to at least 50 Ma and has drifted northward to its present latitude of 29°N since the early Eocene. This latitude history provides a paleomagnetically determined collision age between the Tibetan Himalaya and the southern margin of Asia that is ca. 49.5 ± 4.5 Ma, if not a few millions of years earlier after considering reasonable estimates for shortening within the suture zone. This collision occurred at lat ∼21° ± 4°N, or perhaps ∼2° lower if an average-size forearc is considered. These paleomagnetic data indicate that at most, only 1100 ± 560 km of post-50 Ma India-Asia convergence was partitioned into Asian lithosphere. The lower bound of these paleomagnetic estimates is consistent with the magnitude of upper crustal shortening and thickening within Asia calculated from structural geologic studies. Thus, a substantial amount of the shortening within, and therefore surface uplift of, the Tibetan Plateau predates the Tibetan Himalaya-Lhasa collision. These conclusions suggest that the Tibetan Plateau is similar to the Altiplano of the Andes, in that most of the plateau developed at subtropical latitudes above an oceanic subduction zone in the absence of a continent-continent collision. A direct implication of these findings is that 1700 ± 560 km or more post-50 Ma India-Asia convergence was partitioned into the lower plate of the orogenic system (i.e., units of Indian affinity). Recent paleomagnetic and plate tectonic analyses suggested significant extension of Greater India lithosphere after breakup from Gondwana but prior to collision with the southern margin of Asia. Cretaceous extension within Greater India was inferred to open an oceanic Greater India Basin, which would have maintained a deep tropical water mass along the southern edge of greater Asia throughout most of the Paleogene. We suggest ways in which future climate models can incorporate this paleogeography to more accurately explore how Paleogene atmospheric processes interact with or are modified by the juxtaposition of a tropical ocean basin and the high uniform topography of the Tibetan Plateau.

160 citations


Cites background or methods or result from "Geomagnetic secular variation and t..."

  • ...We evaluate the likelihood that a mean lava-based VGP represents the time-averaged geomagnetic fi eld following Deenen et al. (2011)....

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  • ...The likelihood that a sedimentary paleomagnetic data set represents a time-averaged geomagnetic fi eld direction can be evaluated with reasonable assumptions about geomagnetic fi eld behavior (Deenen et al., 2011)....

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  • ...This can be straightforwardly explained by some averaging of secular variation within individual specimens, which is common in sediments and especially redbeds (Deenen et al., 2011)....

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  • ...…from the site mean directions for most of the individual studies is either greater or smaller than can be straightforwardly explained by the secular variation of the geomagnetic fi eld (e.g., Johnson et al., 2008) and the A95values plot outside of the Deenen envelope (Deenen et al., 2011)....

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  • ...…that the calculated dispersion of this fi ltered mean VGP is consistent with known dispersion caused by paleo secular variation (Johnson et al., 2008), the A95 is within the confi - dence envelope of Deenen et al. (2011), and the pole fulfi lls all seven quality criteria of van der Voo (1990)....

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References
More filters
Journal ArticleDOI
TL;DR: In this article, the authors developed a form of theory which appears to be appropriate to measurements of position on a sphere and demonstrated the simultaneous distribution of the amplitude and direction of the vector sum of a number of random unit vectors of given precision.
Abstract: Any topological framework requires the development of a theory of errors of characteristic and appropriate mathematical form. The paper develops a form of theory which appears to be appropriate to measurements of position on a sphere. The primary problems of estimation as applied to the true direction, and the precision of observations, are discussed in the subcases which arise. The simultaneous distribution of the amplitude and direction of the vector sum of a number of random unit vectors of given precision, is demonstrated. From this is derived the test of significance appropriate to a worker whose knowledge of precision lies entirely in the internal evidence of the sample. This is the analogue of ‘Student’s’ test in the Gaussian theory of errors. The general formulae obtained are illustrated using measurements of the direction of remanent magnetization in the directly and inversely magnetized lava flows obtained in Iceland by Mr J. Hospers.

5,482 citations


"Geomagnetic secular variation and t..." refers background or methods in this paper

  • ...It is common practice to average palaeomagnetic directions using Fisher (1953) statistics; the corresponding VGPs may also be averaged in the same way but this is less commonly done....

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  • ...…of the constructed pole; ϕ = longitude of the constructed pole; α95 = published 95 per cent confidence limits determined on directions; k = published Fisher (1953) precision parameter determined on directions, A95 = 95 per cent confidence limit on the pole, calculated by multiplying α95 by 1.1…...

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  • ...It produces Fisher (1953) distributed sets of VGPs that average to the spin axis and hence supports the GAD assumption....

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  • ...A first milestone paper concerned dispersion of palaeomagnetic vectors on a sphere (Fisher 1953), which enabled palaeomagnetists to determine a statistical mean of a number (N) of directions or poles with an associated dispersion (or precision) parameter (κ , estimated by k or K for directions and…...

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Journal ArticleDOI
TL;DR: The Karakaya marginal sea was already closed by earliest Jurassic times because early Jurassic sediments unconformably overlie its deformed lithologies as discussed by the authors, and it was closed by collision of the Bitlis-Poturge fragment with Arabia.

2,899 citations


"Geomagnetic secular variation and t..." refers background in this paper

  • ...In addition, Europe has undergone little palaeolatitudinal motion since the Eocene, within only a few degrees (Torsvik et al. 2008)....

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  • ...Finally, there is good control on the age and timing of the accretion of blocks to Europe (Sengör & Yilmaz 1981; van Hinsbergen et al. 2005a), which allows us to select only data from those blocks that were already accreted to Eurasia at the timing the sampled sediments were deposited....

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Journal ArticleDOI
TL;DR: In this paper, it is suggested that positive reversal tests should be classified according to the amount of information that was available for the test, which is readily indicated by the critical angle (e.g., at the 95 per cent confidence level) between the two sample mean directions at which the hypothesis of common mean direction for the distributions would be rejected.
Abstract: SUMMARY It is standard practice that a positive reversal test is claimed on the basis of inability to reject the hypothesis that two distributions share a common mean direction, and thus the claim of a positive reversal test is in fact often based on a lack of information. This is unsatisfactory. Therefore it is suggested that positive reversal tests should be classified according to the amount of information that was available for the test. This amount of information is readily indicated by the critical angle (e.g., at the 95 per cent confidence level) between the two sample mean directions at which the hypothesis of common mean direction for the distributions would be rejected. It is recommended that 5", 10" and 20" be used as the breakpoints in the classification.

1,283 citations


"Geomagnetic secular variation and t..." refers background in this paper

  • ...Additional tests have been developed to test whether palaeomagnetic data set share a common mean, such as the reversal test (e.g. McFadden & McElhinny 1990) or, more generally, a common true mean direction (CTMD) test....

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Book
01 Aug 1993
TL;DR: This is the first comprehensive, yet clearly presented, account of statistical methods for analysing spherical data and the emphasis is on applications rather than theory, with the statistical methods being illustrated throughout the book by data examples.
Abstract: This is the first comprehensive, yet clearly presented, account of statistical methods for analysing spherical data. The analysis of data, in the form of directions in space or of positions of points on a spherical surface, is required in many contexts in the earth sciences, astrophysics and other fields, yet the methodology required is disseminated throughout the literature. Statistical Analysis of Spherical Data aims to present a unified and up-to-date account of these methods for practical use. The emphasis is on applications rather than theory, with the statistical methods being illustrated throughout the book by data examples.

1,144 citations


"Geomagnetic secular variation and t..." refers methods in this paper

  • ...We obtained VGP data sets by randomly drawing 10 000 VGPs from a Fisher distribution at the pole (Fisher et al. 1987) with κ values 12.5, 25 and 50....

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Book
01 Oct 1991
TL;DR: Paleomagnetic geomagnetism Ferromagnetic minerals origins of natural remanent magnetism Sampling, measurement, and display of NRM Paleomagnetic stability Statistics of paleomagnetic data PaleOMagnetic poles Special topics in rock magnetism Geochronologic applications Applications to paleogeography Applications to regional tectonics Appendix: Derivations
Abstract: Introduction to geomagnetism Ferromagnetic minerals Origins of natural remanent magnetism Sampling, measurement, and display of NRM Paleomagnetic stability Statistics of paleomagnetic data Paleomagnetic poles Special topics in rock magnetism Geochronologic applications Applications to paleogeography Applications to regional tectonics Appendix: Derivations

933 citations